1. Field of the Invention
This invention generally relates to a hand-held laser scanner for scanning and reading coded indicia, e.g., bar code symbols, with a first scan pattern and, more particularly, to a stand-alone fixture for selectively supporting the laser scanner thereon and, when so supported, for converting the first scan pattern to a different, second scan pattern operative for scanning and reading indicia located exteriorly of the fixture. Furthermore, various digitizer circuits are disclosed for signal processing.
2. Description of Related Art
Hand-held laser scanners are well known. See, for example, U.S. Pat. Nos. 4,387,297; 4,409,470 and 4,806,742 as being representative of the art. A stand-alone laser scanning workstation, for example, see U.S. Pat. No. 4,369,361, having built-in laser, scanning and sensor components is also known.
It is known in this art to construct a digital signal from an analog signal generated from a photoelectric transformation of light reflected off a symbol during scanning by using signal processing digitizing circuits which either use fixed threshold levels derived directly from the analog signal, or which compare a first derivative of the analog signal to a peak signal that follows the peaks of the analog signal. However, such known digitizing circuits are susceptible to errors due to such factors as high ambient light levels and noise, especially in cases where the reading beam spot is poorly focused, i.e., in long-range reading applications, or in reading very high density symbols.